1. Field of the Invention
The invention relates to a photocurable composition and, more particularly, to a photocurable composition which undergoes a curing reaction as a result of a high sensitivity to visible light or near infrared light so as to be employable for a photoresist or in image recording.
2. Description of Related Art
There have conventionally been disclosed in a number of publications many kinds of photocurable compositions curable by visible light, i.e., having a sensitivity to visible light. In general, such a photocurable composition is composed of a polymerizable compound and a polymerization initiator system. The polymerization initiator system generally contains at least a polymerization initiator and a sensitizer dye for modifying a wavelength. The photocurable compositions disclosed in many publications have the following polymerization initiator systems, e.g., composition initiator systems of dyes and aliphatic amines (Japanese Patent Publication No. Sho 44-20189); initiator systems of hexaarylbiimidazoles, radical generators and dyes (Japanese Patent Publication No. Sho 45-37377); initiator systems of hexaarylbiimidazoles and p-dialkylaminobenzylidene ketones (Japanese Patent Laid-open No. Sho 47-2528); initiator systems of cyclic-cis-dicarbonyl compounds and dyes (Japanese Patent Laid-open No. Sho 48-84183); initiator systems of carbonyl compounds and tertiary amines (Japanese Patent Laid-open No. Sho 52-134692); initiator systems employing (keto)coumarin (Japanese Patent Laid-open No. Sho 52-112681); initiator systems of substituted triazines and merocyanine dyes (Japanese Patent Laid-open No. Sho 54-151024); initiator systems of biimidazoles and indanones (Japanese Patent Laid-open No. Sho 54-155292); initiator systems of hexaarylbiimidazoles and p-dialkylaminostilbene derivatives (Japanese Patent Laid-open No. Sho 57-21401); initiator systems of hexaarylbiimidazoles and p-dialkylaminocinnamylidene derivatives (Japanese Patent Laid-open No. Sho 58-19315); initiator systems of triazine derivatives and cyanine dyes (Japanese Patent Laid-open No. Sho 58-29803); initiator systems of triazine derivatives and thiapyrylium salts (Japanese Patent Laid-open No. Sho 58-40302); initiator systems of hexaarylbiimidazoles and n-dialkylstilbene derivatives or p-dialkylaminophenylbutanienyl derivatives and thiol compounds (Japanese Patent Laid-open No. Sho 59-56403); initiator systems of ketone-substituted derivatives and organic peroxides (Japanese Patent Laid-open No. Sho 60-32801); initiator systems of coumarin dyes and diarylidonium salts (Japanese Patent Laid-open No. Sho 60-88005); initiator systems of -diketones and mercapto carboxylic acids (Japanese Patent Laid-open No. Sho 61-258802); initiator systems of xanthene dyes and photopolimerization accelerators (Japanese Patent Laid-open No. Sho 60-221403); initiator systems of -diketones and polysulfides (Japanese Patent Laid-open No. Sho 61-258803); initiator systems of xanthene dyes, radical generators and peroxides (Japanese Patent Laid-open No. Sho 62-143043); initiator systems employing dye borate complexes (Japanese Patent Laid-open No. Sho 62-143044); initiator systems of coumarin dyes and organic peroxides (Japanese Patent Laid-open No. Sho 63-23901); initiator systems employing titanocene (Japanese Patent Laid-open No. Sho 63-41484); and initiator systems employing metal allene complexes (Japanese Patent Laid-open No. Hei 2-296802). These photocurable compositions involve compositions curable with low energy provided by light having wavelengths near those of ultraviolet light, compositions curable with low energy provided by visible light having wavelengths up to about 550 nm, and compositions curable with high energy provided by visible light having wavelengths longer than 550 nm.
The photocurable compositions having a sensitivity to near ultraviolet light or the visible light having wavelengths up to about 550 nm can be cured with low energy, but the photocurable compositions curable by the visible light having wavelengths longer than 550 nm are required to receive high energy for curing. Accordingly, there is a problem that if an ordinary light source is used, a great amount of time is required to provide enough energy, or a high energy, to cure the photocurable composition. There is another problem in that if an operator intends to make a single operation time of the light source as short as possible, the operator must use an expensive light source capable of providing high energy in a short time. In view of the above problems, there has been desired a photocurable composition quickly curable with low energy by an ordinary light source emitting the visible light having wavelengths longer than 550 nm or near infrared light. To meet this desire, the present applicant has proposed, in Japanese Patent Application No. Hei 3-168404 (corresponding to U.S. patent application Ser. No. 07/900,140 which is U.S. Pat. No. 5,275,917 issued Jan. 4, 1994) a photocurable composition employing a metal arene compound and a squalilium dye as a photopolymerization initiator system. The energy for curing this photocurable composition is 4070.49 erg/cm.sup.2, which is considerably lower than the energies for curing any conventional photocurable compositions. However, there is still a need to provide a photocurable composition curable with much lower energy.